1. Field of the Invention
The present invention relates to a galvanic element encompassing a current collector associated with the anode, an anode, a separator, a cathode, and a current collector associated with the cathode. The invention further relates to a battery cell encompassing a galvanic element of this kind, and to a battery encompassing multiple such battery cells.
2. Description of the Related Art
Lithium ion batteries are notable inter alia for a very high specific energy and extremely low self-discharge. Lithium ion cells possess at least one positive and at least one negative electrode (cathode or anode); lithium ions migrate from one electrode to the other electrode as the battery charges and discharges. A so-called “lithium ion conductor” is necessary in order to transport the lithium ions. In lithium ion cells used at present, which are utilized e.g. in the consumer sector (mobile telephone, MP3 player, etc.) or as energy reservoirs in electric or hybrid vehicles, the lithium ion conductor is a liquid electrolyte that often contains the conductive lithium salt lithium hexafluorophosphate (LiPF6) dissolved in organic solvents. A lithium ion cell encompasses the electrodes, the lithium ion conductor, and current collectors that represent the electrical terminals.
The lithium ion cells can be enclosed in a package. Composite aluminum films, for example, can be used as a package. Cells packaged in this manner are also referred to, because of their soft packaging, as a “pouch” or “soft pack.” In addition to the soft pack package design, hard metal housings are also utilized as packages, for example in the form of deep-drawn or cold-extruded housing parts. The term “hard housing” or “hard case” is used in this instance.
Lithium ion cells having a liquid electrolyte are disadvantageous in that under mechanical and thermal stress, the liquid electrolyte component can break down and an overpressure occurs in the cell. Without corresponding protective measures this can cause the cell to burst or even burn.
It is possible to use a solid ceramic or inorganic lithium ion conductor instead of a liquid electrolyte. This concept avoids bursting of the battery cell or leakage of substances upon damage to the package.
Published German patent application document DE 10 2012 205 931 A1 discloses an electrochemical energy reservoir as well as a method for manufacturing it. The electrochemical energy reservoir encompasses at least one electrode assembly in which an ion-conducting and electrically insulating separator layer is embodied on a coated surface. The ion-conducting layer is used as an electrolyte, so that a liquid electrolyte no longer needs to be used. For the embodiment as a lithium ion cell, the active materials proposed for the electrode assemblies are a lithium metal oxide, e.g. lithium cobalt oxide, for the cathode, and graphite for the anode. A ceramic powder having, for example, a particle size of 0.3 to 3 μm, for example lithium garnet, is proposed as a starting material for the ion conductor. The ceramic powder can be applied onto the surface to be coated, for example, in the form of an aerosol.
The use of a graphite anode as proposed in the existing art is disadvantageous because it has only a low energy density compared with an anode based on lithium metal. With lithium metal-based anodes in turn, it is more difficult to implement manufacture of a galvanic element because the metallic lithium is highly reactive, and is stable only in completely dry environments.
When electrodes based on lithium metal are used with the known solid lithium ion conductors, the problem furthermore occurs that a high contact resistance occurs between the metallic lithium and the ion conductor, and thus only small ionization currents can flow. This problem becomes worse once a few charge-discharge cycles have occurred, since lithium ions become dissolved out of the anode upon discharge and the volume of the anode changes as a result.
A good contact that has been made upon manufacture, for example by press-joining, is then lost after a few charge-discharge cycles have occurred, since the lithium metal anode is no longer abutting tightly and with full coverage against the lithium ion conductor.